The Battery: Giving Power when Needed

The cell phones have revolutionalised the way we communicate. The technology of today has lots of uses. Some, like the cell phone, have got some people addicted to its use. Nowadays its hard to communicate with someone without the person occasionally looking at the cellphone. This increased mobility of phones is partly possible courtesy of batteries. Can you imagine the world without batteries? Your non-mechanical/electric clock will no longer keep time, the famous mobile phone will no longer be so mobile if we are constrained to be forever tethered to a wall; and the only mobility is the length offered by the power wires, we will have to find an alternative source of power to kick-start motors to ignite the engine, etc.

We love batteries for many reasons since it allows us easily store direct current until when we need it. Imagine a solar power system without batteries; you will only be limited to use during the sunny day. Emergency equipment like servers, hospital equipment, and businesses like the automated teller machines (ATM) that continually needs power can only easily have that happen without the existence of the battery. In the emergency theatres, lifesaving machines in hospitals hooked to the uninterruptible power supply (UPS) units- a backup power made whole via battery supply.

The simplest battery is the cell, the main unit which is made up of three main parts. They are the two electrodes (one negatively charged anode and the other positively charged cathode) and the electrolytes. The electrolyte is the chemical which through a reaction produces electrons at the anode. The imbalance between the cathode and anode is what creates the electrical or potential difference.

But we have a gatekeeper known as the electrolyte. It prevents the electron-heavy anode from escaping to the cathode side of the battery.

But the gatekeeper opens the door when someone connects a load (e.g. bulb) between the cathode and anode. The electrons will then flow through the connection producing electricity that lights the lamp.

So when the electrons (negatively charged particles) stop flowing to the positively charged cathode, the battery will now be flat or "dead".

For rechargeable batteries, to reverse the process, the battery will "charge" and restore the charged state of the anode, ready for when next a load gets connected which opens up the electrochemical reaction which allows for the flow of electrons from anode until the electrons get depleted. The process is repeated up to a point the battery fails. That time, the anode is unable to hold "charge".

Each battery produced has a certain number of times it can be charged and discharged known as a cycle before it becomes incapable of sustaining charge, i.e. bad. For example, if a battery cycle is 300, it means it can be charged and discharged 300 times before it goes weak/bad or just utterly unable to retain charges.

Depth of Discharge

The battery's longevity is affected by the depth of discharge (DOD). The DOD is a measure of the percentage of the battery's capacity discharged during use. For instance, a 100AH battery that is fully charged (at 100%) has a DOD of 0%, but during use, if the battery lost 25AH of its capacity, it has lost 25% of its total capacity. We can say the DOD is 25%.

Some battery performance is dependent on the level of depth of discharge. Battery capacity can be said to handle 300cylces at 80% DOD of discharge. In other words, if the same battery is discharged up to 90%, the number of cycles will now be less than 300 cycles.

Tesla Powerwall batteries, from the Tesla Electric, uses nickel manganese cobalt oxide (NMC) cells which has 100% DOD capacity and up to 5000+ cycles, little wonder the Tesla Powerwall has a warranty of 10 years.

Ten years is a pretty long time for a battery to last, but if you think that was impressive wait till you meet the rover named Curiosity.

Curiosity Rover, a Battery Life to Envy

I know many wish their laptop battery or their cell phone battery could last a day. This desire is particularly strong in areas like some nations, like Nigeria, still grappling with the problem of electricity scarcity/unavailability; so that one full charge can last all day long. Well, if they are the Curiosity rover on a Mars mission, the wish for a battery that can last more than a day will be adequately fulfilled.

The battery in that rover is capable of powering the spacecraft for 14 years! That was some long time. Remember, unlike other rovers, Curiosity has no solar panel modules, the rover is as big as a car and weighs ten times bigger than its predecessors. The spacecraft engineers opted for this due to some disadvantages of relying on solar power such as decreased performance when dust covers the panel or during winter when there's the shortage of sun.

How did they do it?

The two words that made accounts for this longevity is nuclear and thermocouple.

The thermocouple is when two dissimilar metals have a different temperature between them, one hotter than the other, electricity will flow. We have a German physicist, Thomas Seebeck (1770–1831), to thank for his attempt at heating up dissimilar metals in 1821.

So as you can see, thermoelectric effect, when current is produced via heating up dissimilar metals on different temperature is possible via a thermocouple.

The Curiosity rover uses what the NASA scientist named as Multi-Mission Radioisotope Thermoelectric Generator, or simply MMRTG to run the rover.

The nuclear side of the space battery involves plutonium-238 which during its fission and eventually splitting of atoms produces heat which "cooks up" the thermocouple thereby producing thermoelectric properties in other to generate the electricity needed to power the big Mars explorer.

As you can see, the thermocouple is not a new technology. So also is the RTG technology in space exploration; it was first invented by Mound Laboratories in 1954 by the scientist duo John Birden and Ken Jordan. And first deployed in 1961 as a power source to a 175 pounds (approx 80kg) experimental satellite named Transit 4A.

Why don't we use RTG in our homes?

Though thermocouples are something common in everyday devices such as the refrigerators, air conditioners, and medical thermometers, you won't be seeing the use of an RTG in our home anytime soon. If we ignore the danger (toxicity and radioactive nature) of having a fissionable nuclear material such as plutonium at home, then the cost is crazily high. It costs about $4000 per gram, with terrorists and the likes interested in it, I do not expect the price to be coming down any time soon or even for it to be readily available for purchase.

Curiosity, powered presently, with about 5kg (5000grams) of plutonium-238 which makes the cost of the fuel to be around $20,000,000, a costing which is a conservative estimate as the process of making it is complex and takes a lot of resources.

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^References

• ^{Radioisotope thermoelectric generator}

• ^{How Thermocouples Work}

• ^{Nuclear generator powers Curiosity Mars mission}

• ^{Tesla Powerwall}

• ^{Tesla battery research partner working on longevity breakthrough says work is going into the company’s products}

• ^{Depth of Discharge}

• ^{Power Systems}

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